Field of the Invention
The present invention relates generally to a method and system for on-line monitoring an electrolytic capacitor condition.
Description of the Related Art
In the field of Power Electronics, electrolytic capacitors are known as vulnerable components. Their failure leads to out-of-service condition for the entire converter.
Electrolytic capacitors are often the most limiting factor for long-life products. This is why we observe an increased interest in Condition Monitoring technologies, that permit timely replacement of these components, while disturbance on the service rendered by the equipment is minimised.
Solutions have been proposed to detect ageing of electrolytic capacitors. Usually the ageing detection is made by monitoring the variation of some parameters of the electrolytic capacitor. For example, a reduction of the electrolytic capacitance value may be used to detect the end of life of the electrolytic capacitor, an increase of the equivalent series resistance (ESR) may be used to detect the end of life of the electrolytic capacitor or an increase of the loss factor may be used to detect the end of life of the electrolytic capacitor. The estimation of the parameters may be made by using measurements of the capacitor's voltage and current.
Alternatively some methods require in-depth knowledge of the system, like for example an access to gate drive, converters architecture, information from other sensors in order to avoid to use a current sensor, and to determine the current within the electrolytic capacitor using algebraic calculations.
The ESR of an electrolytic capacitor is a good and reliable ageing indicator since it increases relatively strongly during the life of the electrolytic capacitor due to dry-out of the electrolyte.
Operation at high temperature accelerates the degradation of the electrolytic capacitor.
It has been considered that an electrolytic capacitor is considered aged when its ESR value becomes typically between 2 and 3 times the initial ESR value at the same temperature.